1. Field of the Invention
The present invention relates to a diluting solution for diluting a whole blood sample, if needed, in analyzing a target component or analyte in the quantitative analysis contained in the whole blood sample, using an element for dry analysis. More particularly, it is concerned with a diluting solution and an analytical process using said diluting solution for the quantitative analysis of diluted whole blood samples using, for example, analysis element comprising paper impregnated with a color-producing reagent, or a multilayer analysis element comprising a light-permeable, water-impermeable support having at least one reagent layer and an outermost porous layer.
2. Description of the Prior Art
Dry analysis materials or elements and methods for analyzing quantitatively aqueous liquid samples using them are described in U.S. Pat. Nos. 3,552,928, 3,368,872, 3,036,893, 3,016,292 and 2,846,808, and so on.
Multilayer dry analysis elements comprising a transparent support having thereon at least one reagent layer and a porous layer, in this order, and quantitative analysis methods of aqueous liquid samples using those materials are described, e.g., in, Japanese Patent Application (OPI) Nos. 53888/74 137192/75, 140191/76, 3488/77, 131089/78, 101398/79, 90859/80, 164356/80, 24576/81, etc. (as used herein "OPI" means an "unexamined published application"), H. G. Curme et al and R. W. Spayd et al., Clinical Chemistry, vol. 24, pp. 1335-1350 (1978), Bert Walter, Anal. Chem., vol. 55, No. 4, pp. 498-514, and so on. These references describe the possibility of using non-diluted serum, blood plasma and diluted whole blood as a sample.
More specifically, examples of a clinical test to determine blood glucose using non-diluted whole blood as a sample and a multilayer analysis element as the analysis means are described in Ohkubo et al., Clinical Chemistry, vol. 27, pp. 1287-1290 (1981).
In the clinical application of the whole blood sample analysis using a multilayer dry analysis material, satisfactory analysis results were obtained when fresh whole blood having normal ranges for the hematocrit value and fluidity was employed as a sample. However, it was found that substantial lowering of precision and accuracy of the analysis results occurred frequently when whole blood containing a component to be analyzed in an abnormally high content, having an abnormally high hematocrit value, or having low fluidity was employed as a sample, or whole blood was used as a sample after a several-hour lapse from blood sampling. The above problems did not occur for blood serum or blood plasma, even when the dry analysis method was used. However, rapidity and simplicity of the dry analysis method are lost, since the sample must be centrifuged to obtain blood serum or blood plasma. In determining an analyte in blood, there is much need of obtaining the result of analysis simply and immediately using the whole blood as it is, as a sample, and a dry analysis element as an analyzing implement.
When whole blood containing a component to be analyzed in an abnormally high concentration, whole blood having an abnormally high hematocrit value, or whole blood having low fluidity is handled, it is conventional to dilute the whole blood with an appropriate aqueous diluting solution. When whole blood is diluted, it is desirable that the diluting solution should be a solution having, substantially no hemolytic function, and further, does not cause agglutination of red corpuscles by dilution so that no change in fluidity of the whole blood sample occurs. As for the aqueous diluting solutions having the above characteristics, isotonic solutions containing inorganic salts, such as, physiological saline (including physiological salt solution, Ringer's solution, etc.), and isotonic solutions having a viscosity adjusted properly by addition of a hydrophilic or water-soluble organic substance, such as dextran, polyvinyl pyrrolidone, albumin, etc., to physiological saline have generally been employed. However, whole blood samples diluted with these aqueous diluting solutions exhibit responses different from their neat whole blood samples with respect to, e.g., color development of an analyte applied to a dry analysis element. That is, the analyte concentration calculated by multiplying the concentration derived from the calibration curve determined using neat whole blood samples, by the dilution factor, is not exact. The concentration-dilution factor relationship to correct the above-described error is so complicated that the dilution with the isotonic solutions described above is impractical.